Imagine is the decking over these girders and about 150,000 cars a day whooshing or traffic-jamming their way through. This is where three through lanes from I-95 will meet two from I-91 that meet one from Route 34 out of New Haven.

Welcome to the steel bones of the new eastbound interchange approaching and crossing the new Q Bridge in progress. The state Department of Transportation Tuesday gave a tour of this recently begun latest phase of the interchange project and pronounced all on track a completion of this $357 million phase in the fall of 2016.

“The whole object is to have three dedicated lanes” moving off I-95 to the bridge, said Mathew Briggs, a DOT project engineer who has worked on half a dozen of the 27 separate contracts that comprise the $2.02 billion I-95 New Haven Harbor Crossing Corridor Improvement Program, as it is formally called.

One reason the flyover is so elevated is that the interchange approaches from I-95, and Route 34 will be shooting under it.

In addition to the three travel lanes on I-95 through the interchange, the I-91 to I-95 connections are being enlarged to two lanes wide. That widening at I-91 going south to I-95 has already been completed.

And all the on ramps are being re-designed to lead you into the right-hand side slower lane.

Domenic Larosa, a supervising engineer for the interchange project, said that the challenge will be to build the new lane connections, 12 ramps, and 18 new bridge while demolishing 21 existing structures.

And to do all of it within the same footprint “without shutting down traffic.”

Larosa said that DOT has instituted a new type of planning tool, “3D/4D modeling,” which shows animated construction activities over time. DOT used it during the hoisting of the girders to create the flyover. It permitted engineers to see in advance exactly how it would play out, as the entire operation had to be conducted in three separate 20 minute intervals as traffic was permitted to be stopped only for that amount of time on I-95 in both directions.

He said he expects the interchange project to similarly benefit from real-time modeling. “What if I build this abutment before that? ?ow will it affect traffic?” he asked hypothetically.

He said the modeling will provide a consistent design check and deeper visual understanding as well.

Briggs said that thus far all the complicated and inter-related projects been on time and on budget.

DOT regularly gives such briefings. Tuesday’s was presided over by Larosa and another supervising DOT engineer John Dunham.

The briefing and walk-through occurred at the suggestion of Patricia Drax, a board member of New Haven’s Port Authority.

Drax has been a board member for two years. After the many written briefings on the project, “I wanted to see it,” she said.

A portfolio manager by profession and East Rocker by habitation, she said she became a board member because “I always felt the port and harbor were prized assets.”

In the pre-tour briefing, she asked about the number of the cars the new interchange and bridge are expected to handle in 2016.

“Tough question,” responded Dunham. He and Larosa suggested that the traffic volume for 2016 will be pretty much what it is today, 150,000 cars per day.

“Hasn’t it been shown when we build bigger bridges, the number of cars grows?” Drax asked.

Larosa (pictured) and Dunham suggested there well might be declines in usage as more people use trains and alternate transportation; the creation of the State Street satellite Metro North Station back in 2002 wasthe first completed project in the Harbor Crossing program.

After some concerned discussion, Drax answered her own question: “I suspect we won’t see a slight decrease [in cars on the new bridge] until gas is $10 a gallon.”

The tour, on which she was accompanied by Port Authority Executive Director Judy Shieffele and DOT supervising engineer John Dunham, did not disappoint or disillusion. “I’m much more excited having seen it. I want New Haven to continue to thrive and I think it’s part of the formula,” she said.

Paul Montano, who lives half a block from the Wooster Street on-ramp to I-95, wasn’t so sure. He said he worries that the pile-driving might damage the foundation of his 125-year-old house, once a bottling company started by his uncle, and now his plumbing shop. Montano said he will call DOT about it on Wednesday.